[Encyclios]

Disadvantages

Therefore, even biogas, despite the many advantages listed above, presents problems related to both production and use:

• To power a 1 MW power plant, at least 300 hectares are required, the minimum adoptable area. It is therefore necessary to have large amounts of land available;
• The sewage used gives off unpleasant odors: it is therefore necessary that the plants are located far enough from population centers to ensure a state of comfort to citizens;
• Transport: if the plant is located far away, adequate means of transport will be needed to transport the raw materials, as well as the final products. High traffic involves high carbon dioxide emissions;
• The use of waste biomass and by-products for gas production is not straightforward. Their high fiber concentration can limit digestion by bacteria, which then implies problems related to blending and surface crusting leading to increased self-consumption and reduced plant output.

Like any other technology, biogas has problematic aspects. If we exclude the plants that exploit the biogas produced by the decomposition of organic products from landfills, a large number of biogas plants use animal slurry combined with plant products in a variable ratio, since the yield of biogas is optimized by mixing several types of organic products.

First of all, therefore, for this type of power plants (the most widespread), there is the problem of the raw material. In fact, to feed a 1 MW power plant using only specially cultivated products requires about 300 Ha of available land. Therefore, if this were done on a large scale for many thousands of hectares on valuable agricultural land already used for human or animal consumption, land would be taken away from food production. It is therefore essential that the authorities limit the percentage and type of area that can be cultivated with biomass, in order to maintain a balance between crops dedicated to food or animal feed and crops dedicated to energy production. At the same time, it should also be considered that recent years have been characterized by a progressive abandonment of land due to the low profitability of agriculture and competition from foreign countries.

The substitution of low-income crops with biomass corn or similar plants has allowed many companies to survive this moment of crisis. However, this poses the problem of converting agricultural land for food purposes into agricultural land for energy purposes. In these cases, since the plants needed for fermentation are not intended for human consumption and since what matters is the yield, producers are more encouraged to increase fertilizer and pesticide treatments, thus increasing the environmental impact of the crops involved.

Another problem is related to the bad smells emitted by the fermentation of vegetables and/or the associated slurry. The problem can be solved by a correct management of the plant, in fact the tanks to work must be completely sealed. Many of these plants, usually to exploit the excess heat in a district heating network, are being built far from the areas of production of sewage and close to homes, resulting in heavy discomfort for the population. This involves, among other things, a movement of thousands of trucks only locally because the plants are fed by short supply chain with a consequent decrease in pollution resulting from transport over long distances.